The present invention relates to a magnetic recording and reproducing device and a magnetoresistive device and, more particularly, to a high recording density magnetic recording and reproducing device.
Japanese Unexamined Patent Publication No. Hei 2-61572 discloses a stack layer whose electric resistivity is changed according to an angle of magnetizations of ferromagnetic thin layers separated via an intermediate layer, a magnetic field sensor and a magnetic recording device each using the stack layer, and an iron-manganese alloy thin film.
Japanese Patent Application No. Hei 9-189454 (Japanese Unexamined Patent Publication No. Hei 11-39612) discloses a magnetoresistive device in which a barrier layer is provided between an underlayer made of Ta or the like and a magnetic layer made of NiFe or the like.
Japanese Unexamined Patent Publication No. Hei 6-325934 discloses a spin valve device using a ferromagnetic film made of Co, Ni, Fe, or especially CoFe whose closest packed plane face is oriented perpendicular to the surface.
U.S. Pat. No. 5,408,377 discloses a magnetoresistive device having a free layer consisting of two NiFe layers which are separated by an Ru film.
Japanese Patent Application No. Hei 5-223277 (Japanese Unexamined Patent Publication No. Hei 7-78313) discloses a spin valve layer having a structure of an antiferromagnetic film/a first magnetic film/a nonmagnetic film/a second magnetic film, in which the second magnetic film is a stack layer of Co alloy and Ni alloy, and a magnetic recording and reproducing device.
Japanese Unexamined Patent Publication No. Hei 5-266436 discloses a magnetoresistive sensor having a tri-layer of a first ferromagnetic material thin film layer, a third nonmagnetic metal material thin film layer, and a second ferromagnetic material thin film layer, in which a fourth material thin film layer is disposed in the first ferromagnetic material thin film, on the interface between the first ferromagnetic material thin film layer and the third nonmagnetic metal material thin layer or in a position apart from the interface.
In xe2x80x9cApplied Physics letterxe2x80x9d, Vol. 61, 1992, pp. 1358-1360, an NiFe/Cu multilayer in which a thin Co layer is inserted on the interface is described.
Japanese Unexamined Patent Publication No. Hei 6-236527 discloses a spin valve magnetoresistive sensor in which a back layer made of a nonmagnetic conductive material is stacked to a ferromagnetic layer.
U.S. Pat. No. 5,731,936 discloses a magnetoresistive device using an NiFe film in which an NiCr layer and an NiFeCr layer are stacked.
Japanese Unexamined Patent Publication No. Hei 9-138919 discloses a magnetoresistive magnetic head in which the value of a magnetostriction constant is controlled by adding Au, Pt, or Pd to an NiFe alloy film.
Japanese Patent Application No. Hei 9-1140 (Japanese Unexamined Patent Publication No. Hei 10-198926) discloses a magnetoresistive magnetic head in which the absolute value of a magnetostriction is controlled by stacking a film having a proper magnetostriction on a magnetic film.
Japanese Examined Patent Publication No. Hei 5-37358 discloses a magnetoresistive device in which a magnetoresistive film of positive magnetostriction and a magnetoresistive film of negative magnetostriction are alternately stacked.
According to the conventional techniques, a magnetic recording device of sufficiently high recording density and, especially, a magnetoresistive device, as a reproducing unit of the magnetic recording device, which operates with sufficient sensitivity to an external magnetic field and an output cannot be realized. Further, preferable characteristics such that stability of an output is sufficiently controlled cannot be obtained, and it is difficult to realize the function of a storage.
In recent years, it is known that the magnetoresistive effect of a multilayer in which ferromagnetic metal layers are stacked via a nonmagnetic metal layer, what is called a giant magnetoresistance, is large. In this case, in the magnetoresistive effect, electric resistivity changes according to an angle between the magnetizations of the ferromagnetic layers which are separated by the nonmagnetic layer. When the giant magnetoresistive effect is used for a magnetoresistive device, a structure called a spin-valve is proposed.
Specifically, in the structure of ferromagnetic layer/nonmagnetic layer/soft magnetic layer, the magnetization of the soft magnetic layer rotates by an external magnetic field with respect to the ferromagnetic layer whose magnetization is substantially pinned within a range of the magnetic field to be sensed. Consequently, the electric resistivity changes according to a relative magnetization angle difference and an output can be obtained.
In order to pin the magnetization of the ferromagnetic layer, closely attached antiferromagnetic layer, which generated an exchange coupling field on the ferromagnetic layer in the interface between the ferromagnetic layer and the antiferromagnetic layer is employed. Also, a magnetic film having a large coercive force and a large remained magnetization is employed.
The effect of pinning will be called a pinned bias and the antiferromagnetic film producing the effect will be called a pinned bias film. The ferromagnetic layer whose magnetization is substantially pinned will be called a ferromagnetic pinned layer. Similarly, a soft magnetic film whose magnetization rotates by an external magnetic field will be called a free layer or a soft magnetic free layer.
As described above, the structure of applying a giant magnetoresistive effect and applying a spin valve magnetoresistive stack layer to a magnetic head adapted to high density recording is desirable. The direction of magnetization to be sensed will be called a transverse direction and a direction which is almost perpendicular to the transverse direction and is parallel to the film surface of the magnetoresistive stack film will be called a longitudinal direction. In the case of using it in a magnetic head, generally, the transverse direction is called a device height direction and the longitudinal direction is called a track width direction. Generally, in order to apply a current to the magnetoresistive stack film, a pair of electrodes are disposed in the track width direction and a change in resistance caused by the magnetoresistive effect is detected.
The magnetization state with a zero magnetic field of the ferromagnetic pinned layer has to be in the transverse direction and that of the soft magnetic free layer has to be in the longitudinal direction in a driving state so that the spin valve device has a preferable symmetry as a magnetic sensor. Because of the property that the magnetization of the ferromagnetic pinned layer is pinned, it can be considered that the magnetization of the ferromagnetic pinned layer is relatively directed in the transverse direction.
It is, however, difficult to direct the magnetization of the soft magnetic free layer strictly in the longitudinal direction due to its property that it is rotatable. In the case where the magnetization of the soft magnetic free layer is not strictly in the longitudinal direction, an output of the magnetoresistive device becomes asymmetrical for the positive and negative magnetic fields to be sensed and, simultaneously, an output becomes unstable. The factors related to the stability of the magnetoresistive device are, simply speaking, the magnetic properties of the soft magnetic free layer itself, especially, the magnitude and direction of anisotropy, coercive force, and magnetostriction. In the case where the magnetostriction of the soft magnetic free layer is not zero, when the substrate is distorted, anisotropy induced by stress occurs in the soft magnetic free layer by a reverse magnetoelasticity effect and the direction of magnetization is changed.
One of means to increase the recording density of the magnetic recording is a method of improving the sensitivity to the external magnetic field of the device by reducing the amount of the magnetization of the soft magnetic free layer. A problem especially in such a case is that the magnetic properties of the soft magnetic free layer deteriorate as the film becomes thinner. Specifically, when the sensitivity of the magnetoresistive device is increased to raise the recording density, it becomes difficult to maintain the properties of the soft magnetic free layer preferable and, as a result, the stability of the reproducing device deteriorates. In order to solve the problem, a method of improving the magnetic properties and suppressing the magnetostriction by stacking another magnetic layer on or under the soft magnetic free layer is proposed.
It is an object of the invention to provide a magnetoresistive magnetic sensor and a magnetic recording device adapted to high density recording and, more particularly, to provide a spin valve magnetic sensor having a soft magnetic free layer using a magnetostriction control structure or a magnetostriction control film and a magnetic head and a magnetic recording and reproducing device each using the spin-valve magnetic sensor.
In the invention, as means adapted to high recording density, a magnetic recording device in which a magnetic sensor using a giant magnetoresistive effect is mounted on a magnetic head is employed. As the magnetic sensor, a magnetoresistive device comprising a spin-valve giant magnetoresistive film having a layered structure of soft magnetic free layer/nonmagnetic conductive layer/ferromagnetic pinned layer/antiferromagnetic film is used. The spin-valve giant magnetoresistive film has the layered structure of soft magnetic free layer/nonmagnetic intermediate layer/ferromagnetic pinned layer/antiferromagnetic film and is characterized in that the antiferromagnetic layer applies an exchange coupling magnetic field to the ferromagnetic pinned layer, the magnetization of the soft magnetic free layer rotates according to an external magnetic field, and the relative angle between the magnetization of the soft magnetic free layer and the magnetization of the ferromagnetic pinned layer is changed, thereby producing a magnetoresistive effect.
The subject of the invention is to make the soft magnetic free layer in the magnetoresistive device thinner and to stabilize the magnetic properties. As means to achieve the subject, according to the invention, first, an interface layer for controlling magnetostriction is stacked on the interface of the soft magnetic free layer in the magnetoresistive device. The face on which the interface layer is stacked is the interface opposite to the face on which the soft magnetic free layer is in contact with the nonmagnetic conductive layer. The magnetostriction control film also serves as a diffusion preventing layer for preventing flow of harmful elements from the other layer to the soft magnetic free layer. The diffusion preventing layer may be provided separately from the magnetostriction control film. When the soft magnetic free layer takes the form of a stack member of magnetic films which are different from each other, it is desirable to apply the diffusion/mixture preventing layer on the interface between the magnetic films.
That is, the object of the invention is to realize the structure for suppressing the diffusion from the other film in contact with the interface of the soft magnetic free layer or suppressing the diffusion at the interface of the soft magnetic free layer itself in order to allow the soft magnetic free layer to hold the preferable magnetic properties and a proper magnetostriction value. Another object of the invention is to dispose a film which adjusts elements diffused and flowed through the interface into the soft magnetic free layer to thereby cancel a change in the magnetic properties on the interface of the soft magnetic free layer.
With the structure, by using the magnetostriction control film substantially having no spontaneous magnetization at room temperature, also effects such that an influence is exerted on the soft magnetic free layer disposed via the interface, the value of magnetostriction is made proper, the coercive force is reduced, and the value and the direction of an anisotropic magnetic field are held properly can be produced. Alternatively, by eliminating the influence of diffusing elements flowing in through the interface, preferable inherent properties of the soft magnetic free layer can be held. By mounting the magnetic sensor using the stack film in which the magnetic properties of the soft magnetic free layer are improved by using the means as mentioned above, the magnetic head and the magnetic recording and reproducing device having a preferable output and stability can be obtained.
As another solving means, an interface control layer for preventing mixture and diffusion is inserted between an Ni alloy layer and a Co layer constructing the soft magnetic free layer. The material and the thickness of the interface control layer are selected so as to suppress increase in the magnetostriction caused by the mixture of Ni and Co and so as not to deteriorate the magnetic connection between the Ni alloy layer and the Co layer and transmittance of electrons to generate magnetic resistance.
It is noted here that, although each of the interface control layer, the magnetostriction control layer, and the mixture/diffusion preventing layer is described as a layer, it denotes a process of forming each of them as a layer when the stack film is formed. Even when each of the layers is not a complete continuous layer or diffusion or mixture occurs with the neighboring layer, the function is not lost at all. Rather, the mutual action with the neighboring soft magnetic free layer is also desirable.